1. Field of the Invention
The present invention relates to information transfer in a system comprising at least three subsystems, and more particularly to an information transfer system suitable for use in various management and/or control systems such as a building control (supervisory) system, a steel production system, or a train operation management/control system.
2. Description of the Prior Art
Japanese Patent Laid-Open No. 64-32597 and No. 1-135290 disclose such a centralized control system wherein a centralized control unit has input and output terminals for external signals and contact signals, and the system includes a means capable of operating and stopping all equipment connected to the system based on the external signals and also of indicating these states of operated/stopped conditions of the equipment to the exterior, without actuating the centralized control unit.
Recently, the main types of management/control systems have been distributed ones aiming to achieve fine monitor control and reduce the burden on a central processing unit.
Japanese Patent Laid-Open No. 64-30397 discloses information transfer processing for distributed systems, inclusive of interlock (cooperation) processing. This prior art describes a control system comprising a central processing unit, a plurality of equipment control units and a plurality of monitor control units for the purpose of interlock processing. The central processing unit has a data management means for managing correspondence between the interlocked control processes, and an interlock data output means for outputting interlock data, whereas the monitor control unit has an individual identification means.
Meanwhile, as represented by office automation (OA), there has also been proposed an integrated system with various business support systems, business management systems and so forth connected, as subsystems, to a central processing unit. Along these lines, Japanese Patent Laid-Open No. 2-69096 discloses interlock control between an OA system and a control/supervisory system of building facilities.
Of late there has been demand for such an integrated building control system that the above-described integration and distribution types are combined with each other based on the concept of "integration of management/distribution of monitor control". The integrated building control system is one in which systems for building management, security, etc. are integrated, as subsystems, into a central processing unit or the like of a distributed building control system.
The above various forms of integrated systems in the prior art require a unified information transfer technique, i.e., an information communicating technique, not depending on the system forms.
The above-cited Japanese Patent Laid-Open No. 64-32597 and No. 1-135290 illustrate examples in which a contact signal, i.e., an on/off signal, is used as external inputs and external outputs of the centralized control system. Even in the case of sending simple information, therefore, it is imperative to provide a plurality of external input/output terminals and give the respective terminals specific meanings, resulting in limits of system extension. Furthermore, the prior art centralized control system of that type was able to transfer simple information, i.e., on/off information of contacts, among the limited systems, but not able to adapt for transfer of complex information among various systems in intelligent buildings or the like.
The information transfer processing of the above-cited Japanese Patent Laid-Open No. 64-30397 is intended to further reduce the burden on the central processing unit. But, because of incapability of interlocking the subsystems through information transfer among the subsystems integrated into the central processing unit, this prior art information transfer processing could not be applied to an integrated system.
In addition, since interlock data is previously sent to each of terminal units to be interlocked through the information transfer for interlocking the terminal units without intervention of the central processing unit, the interlock data necessary for each interlock must be stored in both the interlocking unit and the interlocked unit. Accordingly, interlocking a number of terminal units needs very large storage capacity for each unit and increases a load to be processed for the interlocking. This leads to a difficulty in processing of the monitor/control unit which requires real-time processing in its nature.
The above-cited Japanese Patent Laid-Open No. 2-69096 describes an interlock system in which various systems equipped in a building are connected to various OA systems equipped in offices through communication lines, and information for controlling facilities and equipment in the building are transferred from one system to another so that automatic coordinated operation may be performed between the systems without needing the attention of users. However, this prior art does not disclose a decision means for sending transfer information received from one subsystem to another system.
An object of the present invention is to provide a universal information transfer system which is not restricted by specifications of subsystems making up a target system, and also which does not restrict the specifications of those subsystems as far as possible.